(1) Field of the Invention
The invention relates to a method of etching of metal lines, and more particularly, to a method of cleaning metal precipitates after the etching of metal lines in the manufacture of integrated circuits.
(2) Description of the Prior Art
Aluminum and aluminum alloys are often used to form metal lines in integrated circuit processing. To prevent aluminum spiking, a barrier metal layer comprising titanium, titanium nitride, titanium tungsten, or the like, is deposited underlying the aluminum layer. The aluminum layer is etched away where it is not covered by a photoresist mask to form the desired aluminum lines. A metal precipitate forms during aluminum layer deposition at the interface of the aluminum and barrier metal layers. The precipitate may comprise such materials as Al, Si, Cu, Ti, W, and the like, such as TiAl3, AlCux, WAl5, silicon nodules, copper nodules, etc. Typically, the metal precipitates are cleaned away using a sputter etch. However, not all of the precipitates can be removed by this method. For example, TiAl3, WAl5, or AlCux precipitates cannot be removed by sputtering alone.
U.S. Pat. No. 5,238,872 to Thalapaneni teaches the use of a reduced amount of Cl2 in an overetch to remove residual metal stringers. U.S. Pat. No. 5,413,669 to Fujita teaches etching away an unwanted alloy using an etchant gas. U.S. Pat. No. 5,641,382 to Shih et al discloses the use of an ion beam to remove silicon nodules after aluminum etching. U.S. Pat. No. 5,200,361 to Onishi uses a mixed gas of HF and N2 to remove aluminum deposits in a via hole. U.S. Pat. No. 5,350,488 to Webb discloses a low pressure, low temperature etching to prevent copper residues. U.S. Pat. No. 5,360,510 to Kadomura teaches the use of BCl3, Cl2, and HBr in etching aluminum.